It's not for me, but I think it has a bit of nerdy-crusty-hipstery charm like Myrtle or Hazel or Prudence or Agnes or Ethel...somehow all of these feel more popular than Gladys. I say use Gladys. Maybe you'll start her comeback!

I suppose I don't like Gladys because it's "old," though I try to keep an open mind. I've had this conversation with myself before, and I can't really think of any other reason to dislike it! It has the word "glad" in it, and I like other -ys-ending names and Welsh names in general. Right now it would probably be best in the middle, although if you name a baby Gladys in the next year or two, by the time she's a teenager the name might be cool again.

"He telleth the number of the stars; He calleth them all by their names."
Psalm 147:4

I'd keep it as a middle name because it has meaning to you, but I really don't think this one would go over very well :/ (That being said, the names I want to comeback likely won't go over well either...)